Fall Bright has been providing winemaking supplies, grapes, juices (plus brewing supplies) for  amateur winemakers for over 20 years.  
An old grape packing house provides a home for Fall Bright.     

Fall Bright, The Winemakers Shoppe, 10110 Hyatt Hill, Dundee, NY 14837
607-292-3995 

Bocksin:  Silicium Dioxide  SiO_{2
Silicon (English) Dioxide
Silicium (Latin) Dioxide}

Kieselsol is the commercial name for liquid silicon dioxide.

When hydrogen sulfide is formed in detectible quantities, it will usually be toward the end of fermentation.  You should smell your young wine during the first fermentation.  If the rotten egg smell is evident, you should pre-treat the wine immediately, when the problem is first discovered.

1.      Dose the wine with the recommended amount of a yeast nutrient.  It may be best to dissolve the nutrient in water or wine to ensure homogeneous mixing. 

2.      Rack your wine even if it is still fermenting.  If the smell hasn't disappeared in 24 hours, rack again.  Aerate and splash about.  

3.      You may also bubble an inert gas such as carbon dioxide or nitrogen through the wine.

4.      If the above steps do not correct the problem, you may wish to use Bocksin or Copper Sulfate. 

Böcksin, silicate liquid, dispensed in 4 oz bottles (118 ml), is used to eliminate or reduce hydrogen sulfide and mercaptan odors in wine without having to resort to treatment with copper, except when fairly high H2S levels are present.

Typical usage is 2 to 6 ml per gallon. A teaspoon is 5 ml.  Treatment duration is 24 to 48 hours.  Mix briefly about four times a day. A bench test is strongly recommended to determine dosage.

 
The intensely smelling sulphur compounds are bound and sulphur-tannin compounds are precipitated. The treated wine should be racked and filtered before it is tasted to remove precipitated and bound compounds resulting from treatment. 

Finings recommended after use are gelatin, LQ Super-Kleer KC Finings, isinglass, bentonite, Sparkolloid. 

There is no recommendation to wait for the end of fermentation to treat the wine with Bocksin.

It is compatible with copper sulfate treatment should that be necessary. 

Bocksin separates during storage and should be well shaken before use to insure uniformity.

Treatment for hydrogen sulfide: (from the label, English as a second language) 
Bocksin (FROM the label): "is a solution of Silicium Dioxide for treatment of hydrogen sulfide odors and related off-flavors in wine. Usage is 15 ml per ten liters (2.75 gallons). Stir thoroughly and wait 24 hours. Rack without disturbing the sediment. 

The current label does not indicate filtration but to allow settling.  

It is not necessary to filter the wine after treatment. If the wine becomes cloudy, treat with finings.

1 USA gallon is 3.84 liters, 1 teaspoon is 5 ml, regarding the above text that 10 liters is 2.75 gallons is a rough figure with rounding off factors, I get 2.6 gallons per 10 liters. Anyway we would treat 5 US gallons with 30 ml or 6 teaspoons or 2 tablespoons of Bocksin.

So What is Silicium Dioxide?  http://www.vanderkrogt.net/elements/elem/si.html 
Silica, Silicium Dioxide, Silicion Dioxide
This link would have been great in chemistry class!  I did not copy it nor did I request permission to do so, but do check it out.  Our winemakers are worried about toxic chemicals for use and I feel safe with this item.  Read your grocery item labels in the spice department and you will find that you eat a lot this item!  Marcy